The development of new medical technologies has provided an increasing number of options available to doctors for the diagnosis and treatment of cardiovascular diseases. The availability of such equipment has improved the ability of doctors and surgeons to detect and treat cardiovascular disease. Intravascular imaging technologies have enabled doctors to create and view a variety of images generated by a sensor inserted within a vasculature. Such images compliment traditional radiological imaging techniques such as angiography by providing images of the tissue within vessel walls rather than showing a two dimensional lumen image.
Intravascular ultrasound (IVUS) analysis finds particular application to a system and method for quantitative component identification within a vascular object including characterization of tissue. It should be appreciated that while the exemplary embodiment is described in terms of an ultrasonic device, or more particularly the use of IVUS data (or a transformation thereof) to characterize a vascular object, the present invention is not so limited. Thus, for example, using backscattered data (or a transformation thereof) based on ultrasound waves or even electromagnetic radiation (e.g., light waves in non-visible ranges) to classify tissue according to a type or composition is within the spirit and scope of the present invention.
Imaging portions of a patient's body provides a useful tool in various areas of medical practice for determining the best type and course of treatment. Imaging of the coronary vessels of a patient by techniques involving insertion of a catheter-mounted probe (e.g., an ultrasound transducer array) can provide physicians with valuable information. For example, the image data indicates the extent of a stenosis in a patient, reveals progression of disease, helps determine whether procedures such as angioplasty or atherectomy are indicated or whether more invasive procedures are warranted.
In an ultrasound imaging system, an ultrasonic transducer probe is attached to a distal end of a catheter that is carefully maneuvered through a patient's body to a point of interest such as within a coronary artery. The transducer probe in known systems comprises a single piezoelectric crystal element that is mechanically scanned or rotated back and forth to cover a sector over a selected angular range. Acoustic signals are transmitted and echoes (or backscatter) from these acoustic signals are received. The backscatter data is used to identify the type or density of a scanned tissue. As the probe is swept through the sector, many acoustic lines are processed building up a sector-shaped image of the patient. After the data is collected, an image of the blood vessel (i.e., an IVUS image) is reconstructed using well-known techniques. This image is then visually analyzed by a cardiologist to assess the vessel components and plaque content. Other known systems acquire ultrasound echo data using a probe comprising an array of transducer elements.
In a particular application of IVUS imaging, ultrasound data is used to characterize tissue within a vasculature and produce images graphically depicting the content of the tissue making up imaged portions of a vessel. Examples of such imaging techniques based on spectral analysis of ultrasound backscatter data and color-coded tissue maps are presented in Nair et al. U.S. Pat. No. 7,074,188 entitled “System and Method of Characterizing Vascular Tissue” and Vince et al. U.S. Pat. No. 6,200,268 entitled “Vascular Plaque Characterization”, the contents of which are incorporated herein by reference in their entirety, including any references contained therein. Such systems analyze response characteristics of ultrasound backscattered (reflected sound wave) data to identify a variety of tissue types (also referred to as “plaque components”) found in vessel occlusions including: fibrous tissue (FT), fibro-fatty (FF), necrotic core (NC), and dense calcium (DC).
When characterizing the response of tissue when exposed to ultrasound waves, parameter values are considered at a data point in an imaged field. Based upon response characteristics of known tissue types, tissue at the data point is assigned to a particular tissue type (e.g. necrotic core). The set of character data points in an imaged field are thereafter converted into viewable cross-sectional image wherein the various identified types of tissue are presented in a color-coded form for clinical analysis. In a particular known system, the detected area of a cross-sectional “slice” of an imaged vessel occupied by each tissue type is calculated. For example, upon completing a tissue characterization analysis, the system renders cross-sectional areas occupied by dense calcium, fibrous, fibro-fatty, and necrotic core tissue. Furthermore, the compositional information generated at each cross-sectional slice during a pull-back procedure is stored as a series of data sets, and the composition of the various plaque classes at each slice is graphically represented two-dimensionally as plaque composition (area) at each slice covering a series of sequential blood vessel cross-sections.
While the known tissue characterization systems provide visually discernable features, the importance of each type of plaque tissue, including its overall amount, confluency, and position in the cross-section is subject to the personal experience and training of each viewer. Thus, two individuals viewing a same cross-sectional image potentially come to significantly different diagnoses and proposed courses of treatment.